Negative pressure wound therapy (NPWT) is the use of sub-atmospheric pressure to assist wound healing, or to remove fluids from a wound site. As the conventional NPWT system shown in FIG. 1, the NPWT system comprises: a patch 200 sealing a wound 500; a flexible suction disc (not shown in the figure); a bio-compatible porous wound dressing 300; a drainage tube 310 placed adjacent to or inserted in the dressing 300 for connecting the wound 500 to a spent liquid container 600; and a connection tube 110 connecting the spent liquid container 600 to a vacuum source 100; by which a negative pressure is applied to the wound 500 in the flesh 400. The concept is to turn an open wound into a controlled, closed wound while removing excess fluid from the wound bed, thus enhancing blood circulation and disposal of cellular waste from the lymphatic system for assisting wound healing.
The designing principle of the cascade-like connection of the dressing 300, the spent liquid container 600 and the vacuum source 100 is to prevent the vacuum source 100 from being contamination. However, the aforesaid conventional NPWT has the following shortcomings:                (1) As the spent liquid container 600 is connected to the vacuum source 100 by the connection tube 110 with a length, not only the connection tube 110 is too long may the cause of inconvenience, but also it is difficult to prevent the same from leakage and thus may cause the performance of the vacuum source 100 to drop.        (2) Considering factors such as power, noise, and lifespan, the vacuum source 100 must adopt high-power motor, but the vacuum source 100 using high-power motor not only is overweighted, but is expensive.        (3) As the power consumption of the vacuum source 100 using high-power motor is comparatively higher, larger battery module 700 should be used that further cause the whole NPWT system to be larger and heavier.        (4) As the spend liquid container 600 should be designed with a volume, not only it is lumpy and may take up quit a few space, but also it may cause difficulties for moving the NPWT system.        (5) There can always be a potential hazard that the spent liquid container 600 may be tilted for causing the spent liquid storing therein to pour out and thus contaminate the whole NPWT system.        (6) The aforesaid NPWT system is too large and heavy that it is not portable so as to be carried by a patient.        
There are already some studies trying to improve the conventional NPWT system. One of which is an appliance for administering a reduced pressure treatment to a wound, disclosed in U.S. Pat. No. 7,216,651, entitled “Wound treatment employing reduced pressure”. However, the aforesaid appliance still adopt the conventional cascade-like connection of the dressing, the spent liquid container and the vacuum source 100 so that it is complex and expensive.
Another such study is an apparatuses for evacuating body fluids, disclosed in U.S. Pat. No. 5,549,584, entitled “Apparatus for removing fluid from a wound”. In the aforesaid apparatus, the dressing covering a wound is connected to a bellows pump while the bellows pump is then being connected to a collection bag that is different from the aforesaid conventional NPWT system, i.e. the dressing is connected to the pump and then the pump is connected to the collection bag. It is only suitable for treating wounds with small opening despite of it is ease to operate, since the negative pressure of the aforesaid apparatus is generated by the operation of the bellows pump in a manual manner that can not be controlled accurately.
Yet, another such study is a wound dressing apparatus disclosed in U.S. Pub. No. 2007/0055209, entitled “Self contained wound dressing apparatus”. The components used in the apparatus is connected in a manner that is similar to the apparatuses disclosed in U.S. Pat. No. 5,549,584, i.e. the dressing is connected to the pump and then the pump is connected to the collection bag. The difference is that, instead of the bellows pump, the wound dressing apparatus uses an external peristaltic vacuum pump which can only generate a comparatively smaller vacuuming force. Any intension for increasing vacuuming force will require the wound dressing apparatus to use larger external peristaltic vacuum pump, however, it is going to cause the volume of the wound dressing apparatus to increase.